Water soluble polyacrylamides (PAMs) have been proposed as soil amendments for various agricultural purposes. Water soluble polymers, generically described as polyacrylamides (PAMs) appear to have a variety of beneficial soil amendment properties, including minimization of water run-off, erosion, and crusting, stabilization of soil structure, and binding of nutrients and microbes within soil.
Since the late 1980's there has been renewed interest in the use of water soluble polymers for soil physical improvement. Although PAM has been used for soil structure improvement since the 1940's and in agriculture since the 1950's the kinds of PAM used and the methods of application were different. Early PAMs had lower molecular weights than today's PAMs. They were applied to the soil at high rates, and were incorporated into the top soil by tillage.
In addition to the current interest in anionic PAMs as soil conditioners, they are widely used for other applications. PAMs are used for mineral and coal processing, petroleum production, paper making, water treating, food processing, and other miscellaneous applications.
Polyacrylamide is a synthetic water-soluble polymer made from monomers of acrylamide. It binds soil particles in the water and irrigated furrow together, making particles larger so the water has a harder time washing them out of the field.
Polyacrylamides are compounds that hold on to nutrients and troublesome microbes before they can escape from soil and make their way to ponds, lakes, streams, rivers, and/or ground water. PAM has been shown to help keep nutrients, such as nitrogen and phosphorous in fertilizers, from traveling beyond the farm in irrigation runoff. Similarly, PAM helps keep disease causing microbes, like those in cow, pig, or fish manure, from being swept beyond the confines of farmyards or feedlots.
PAM's three most common forms are dry granules, solid blocks (cubes) and emulsified liquids. The application method of PAM chosen depends on the form of PAM selected.
The use of dry granular PAM into irrigation water requires the use of an augured metering system and excellent mixing and thorough dissolving before the PAM reaches the irrigated furrows. Dry granules of PAM can be applied either by dissolving directly in the irrigation ditch before it hits the furrow, or applied directly in the furrow using what is known as the “patch method”. The patch method involves placing PAM at the point in the furrow where the water first hits; applying it for a length of about 3-5 feet down the furrow to reduce the risk of the PAM becoming buried in the furrow or washing down the furrow with little to no effect. The patch method creates a sort of gel-slab at the top of the furrow where the water slowly dissolves the PAM and carries it down the furrow.
In order for the PAM to dissolve into a liquid properly in the irrigation ditch it must have proper agitation. Unlike sugar or salt which dissolve fairly quick in water, granular PAM needs to be agitated thoroughly in order for it to dissolve. If not agitated, PAM globules form, and in time the globules can float down the furrow with little effect on the furrow erosion. A way to make sure the applied PAM is dissolved is to have a drop structure in the ditch to add turbulence to the water before it hits the furrow. Another tip to achieve desired dissolving is to apply it close to the point where the irrigation water first hits the ditch. In a concrete ditch, tins or boards will provide sufficient turbulence. In an earthen ditch a drop dam works nicely.
There are many known problems for applying PAM to the soil using present applications. The dry formulation is easy to handle, but must be kept dry due to its affinity for moisture. The dry material is primarily used for open ditch application due to the difficulty of getting the material into a water pipeline. For best results, the applicators used to dispense the bulk material are placed upstream of the irrigation set and away from any splashing water droplets.
When exposed to humidity, polyacrylamide granules tend to stick to each other and to drop tubes which can then plug. The flow rate for granular PAM ranges from 2 to 33 grams per minute depending on irrigation flow and desired concentration in the irrigation water. A small error in the rate of metered PAM will lead to large differences in concentration in irrigation inflow water. Dry PAM applicator considerations include: dispensing rates of 1 to 35 grams/min; precalibrated or easily calibrated for fast setup in the field; portability; lasting power supply.
With a closed pipe system, the liquid formulation is normally recommended. Using an injector pump, the liquid can be pumped directly into the irrigation pipeline. Turbulence in the pipeline, such as an elbow, helps mix the PAM with the water. The natural turbulence in a pipeline 100 feet long or greater is likely sufficient for mixing. The liquid material is, however, difficult to handle outside of the container. To clean up anything that has come in contact with liquid PAM, it is common practice to “wash” the PAM off with soil. The PAM will adhere to the soil particles making cleanup with water possible.
The liquid formulation also can be used for open ditch applications; however, if a pump is not being used, and the liquid dribbles into the water, the viscosity of the liquid can change with temperature changing the calibrated delivery rate. Keeping the containers out of direct sunlight will reduce, but not eliminate, this problem.
Liquid PAM can be metered directly from the container into the irrigation ditch, directly into the furrow, or through a pipe line or injector pump. Emulsified PAM (special liquid PAM solutions) can be applied like the granular form into irrigation ditches or into furrows using the patch method. Emulsified PAM doesn't require quite the vigorous mixing as the granular form, but still needs adequate mixing for dissolving. Emulsified PAM is more voluminous than dry forms, but has an easier time dissolving and is the only form of PAM that should be used for sprinkler irrigating systems, due to greatly reduced the risk of clogging the lines.
The solid formulation of PAM is placed in an area where turbulence is occurring. The action of the water slowly dissolves the polyacrylamide into the flowing water. The only way to control the amount added into the water is to control where the solid PAM is placed and how long it is left in the water. Calibration for dispersion rate has not yet been determined, so trial and error is the current method used.
PAM blocks (or cubes) are usually placed in wire baskets in flowing ditches at turbulent points. The wire baskets need to be secured to the edge of the ditch to avoid washing of the blocks down the ditch. The blocks slowly dissolve, releasing small amounts of PAM into the water. Of the three forms PAM blocks may not perform as well as liquid or granular PAM in furrow irrigation. PAM blocks, however, have been useful for treating settling ponds to accelerate water clarification and promote flocculation. They can also be used to dose concentrated runoff areas on fields that otherwise cause uncontrolled erosion.
Adding polyacrylamide to water is much different than adding most other materials. For example, if a cup of salt water is added to a gallon of water and stirred, the salt will, in a short period of time, dissolve. However, when polyacrylamide is added to water, turbulence is necessary to ensure adequate mixing. Without adequate mixing, the polyacrylamide will not immediately dissolve and PAM globules will form. In time, these globules will find their way to the field and can be seen floating down the furrow. Although not as likely, globules do still occur with injector system use. If PAM is being applied with a center pivot, sprinkler nozzle, plugging may occur if the PAM solution is not well mixed.
The application method depends on the material selected. Granular PAM requires some form of augured metering system. Solid blocks should be placed in a wire basket and secured to the side of the ditch to avoid washing the block downstream. Liquid PAM can be metered directly from the container into an open ditch or through an injector pump into a pipeline.
If adding either liquid or dry PAM to an open ditch, the discharge point is kept at least 2 feet away from the flowing water. Small droplets of water can cause the PAM to clog at the outlet and stop flow. If turbulence in the water is causing splashing, the applicator is moved away so that the water does not contact the container or move the turbulent flow downstream.
Another concern, is the type of water used for irrigation. Because polyacrylamide attaches to the soil particles and binds them together, water containing a lot of sediment may result in sediment settling out before water is diverted into the furrows. In general, this does not affect PAM's effectiveness, but with extremely sediment-laden ditch water, sediment may build up and restrict flow in the supply ditch. This is also a concern for underground transport pipes. If the water velocity in the pipe is insufficient to lift the accumulated sediment, pipe flow may be restricted. Though the pipe flow rate is reduced, the pipe is not likely to plug completely, since as the sediment decreases the pipe's inside diameter, water velocity increases.
Different soil textures and field slopes can give different results when receiving equal quantities of PAM. One can start with the 10 ppm rate and increase or decrease the concentration based on the clarity of the runoff leaving the field.
For maximum effectiveness, thoroughly mix PAM with the irrigation water before application. In an open ditch, let the water pass over at least one drop structure or some ditch obstruction to cause turbulence before water is diverted into the furrows. In an earthen ditch, a drop dam will suffice; in a concrete ditch, boards can be used to create the turbulence. In some cases a drop is created in order to adequately mix the material in water. In gated pipe, the pipe swirling action will generally cause enough mixing within the first 2-3 pipe joints. If pressure in gated pipe is relatively low, 3 feet or less, a Krause Box can be used to create a drop structure in the pipeline.
Regardless of what form of PAM is supplied to the farmers (dry material, concentrated material, or pre-mixed stock solution) it is important to provide aggressive mixing (agitation) at the point of application of PAM to the water sources. The agitation requirement increases as the concentration of stock solution increases and is greatest for use of direct dry PAM application. Agitation should be provided by use of a stream drop and multiple flow obstructions near the point of injection. With vigorous turbulent flow 25-50 ft of ditch canal should be allowed for stock solution mixing before the first siphon tube withdrawal or gate. Dry PAM may need longer ditch runs for adequate mixing. If using gated pipe, the first length of gated pipe after the point of PAM injection should have one or two baffles to enhance mixing. PAM should not be added upstream from weed screens or filters of any kind. Heating of water of stock solution greatly enhances PAM dissolution and mixing.
The furrow is considered treated once the water reaches the end of the field, and additional polymer is normally not required for that irrigation. In many cases, producers have found that, rather than applying PAM until water advances to the end of the field, protection is adequate by applying PAM only until water advances 50 percent or less of the field length. The advantages are erosion control in the top portion of a field, reduction of sediment deposits in the bottom portion of the field and reduced application costs.
Because polyacrylamide attaches itself to the soil near the surface, cultivation or ditching after PAM application results in loss of effectiveness. PAM should be reapplied after cultivation or ditching disturbs the soil surface. Once applied, PAM is not effective all season long. However, after the initial application, PAM does continue to offer some erosion control during subsequent irrigations. Factors, such as soil type, field slope and irrigation furrow stream size, will determine the long-term effectiveness of a single PAM application.
Inadequate mixing of PAM may result in highly concentrated PAM being applied in the first few furrows and insufficient PAM in the furrows furthest from the point of injection.
The use of automated timers or liquid shutoff valves can be problematic for controlling PAM injection because it is difficult to accurately predict furrow advance time. If advance time is slower than expected, the bottom portion of the fields will not be treated with PAM. If furrow advance is faster than expected more PAM than necessary will be applied and PAM losses in runoff water could occur.
If using PAM in sprinkler irrigation, the pipes must be pressurized to be sure water is delivered before injecting PAM into the flow. This protocol assures that PAM does not build up in sprinkler lines before water enters the pipes (which would violate the caution of not adding water to PAM). Benefits of using PAM with sprinkler irrigation are much less dramatic than with furrow irrigation. Applying 2-4 lb PAM per acre can reduce erosion and increase infiltration during the irrigation under some conditions. However, beneficial effects last for only one or two irrigations.
PAM treatment has usually been by injection of small amounts of concentrated stock solutions into the irrigation water supply. There is some indication that direct powder addition may be feasible, but the concept has not been extensively tested. PAMs are applied via irrigation water to only that small part of the soil that play a role in the physical processes of erosion, sealing and crust formation.
Water-applied PAM increases soil cohesion and strengthens the aggregates it contacts in the furrow by binding exposed soil particles together more securely. This greatly reduces detachment and transport of sediments in irrigation runoff. Soil erodibility at the soil water interface is reduced by improved inter-aggregate bonding and better maintenance of surface roughness. PAM also acts as a settling agent. It flocculates (clumps together) the fine particles. If an irrigation is not adjusted, over-wetting of the upper and/or underwatering of the lower ends could be worsened.
Most states require that agricultural chemicals (including soil amendments such as PAM) meet safety and state labeling requirements. The PAMs currently labeled are water soluble, anionic (11-20%), high (10-15 million) molecular weight compounds meeting EPA and FDA monomer limits below 0.05%. PAM is available in several forms: dry powder or granules containing 80-95% active ingredient (AI); inverse oil-emersion liquid concentrates containing 30-50% AI (PAM is dissolved in water droplets that float in an oil matrix); and pre-mixed PAM-water solutions containing <3% PAM.
At a minimum PAM should be used on the first irrigation and when soil is disturbed by traffic and/or cultivation. Additional applications at or below label amounts may be considered to provide complete erosion control for the entire season. If PAM is applied in the first irrigation and subsequent irrigations have no PAM in the water, then erosion control and infiltration effects can be expected to decline approximately 50% with each non-treated irrigation. Thus, by the third irrigation, little effect remains. For those crops in which erosion naturally subsides during mid season, PAM need not be applied after the natural erosion reducing properties ensue.
Polyacrylamide (PAM) is a long-chain molecule commonly used to clean waste water. To date, the primary market for this compound has been municipal wastewater treatment facilities. It makes the fine solids in treated water glom onto one another, until they become big enough to settle out or be captured by filters to make sewage sludge.
PAM seeks out and binds to the broken edges of clay particles, which carry a negative charge. By increasing the cohesiveness of soil particles on the soil surface of a field, PAM makes dirt more resistant to the highly erosive shear forces exerted by water flowing over it. This binding is referred to as flocculation. Flocculation is used to describe the action of polymeric materials which form bridges between individual particles. Bridging occurs when segments of a polymer chain adsorb on different particles and help particles aggregate. Flocculants carry active groups with a charge which will counterbalance the charge of the particles. Flocculants adsorb on particles and cause destabilization either by bridging or charge neutralization. An anionic flocculant will usually react against a positively charged suspension (positive zeta potential). That is the case of salts and metallic hydroxides. A cationic flocculant will react against a negatively charged suspension (negative zeta potential) like silica or organic substances.
The most common polymers are those based on polyacrylamide, which is a nonionic polymer. Their effect is due to bridging between particles by polymer chains. Polymers can be given anionic character by copolymerizing acrylamide with acrylic acid. Cationic polymers are prepared by copolymerizing acrylamide with a cationic monomer. All available acrylamide based polymers have a specific amount of ionic monomer giving a certain degree of ionic character. They have a specific average molecular weight (i.e. chain length) and a given molecular distribution. For each suspension, a certain degree of anionic, cationic or nonionic character is beneficial. Usually, the intrinsic flocculating power increases with the molecular weight. Polyacrylamides have the highest molecular weight among the synthesized industrial chemicals in the range of 10-20 millions. Other polymers display specific properties and are used under specific conditions. They are mostly: Polyethylene-imines, polyamides-amines, polyamines, polyethylene-oxide, sulfonated compounds.
Anionic PAM are “Off the Shelf” Industrial Flocculants used extensively for: potable water treatment, dewatering of sewage sludges, washing and lye-peeling of fruits and vegetables, clarification of sugar juice and liquor, adhesives and paper in contact with food, animal feed thickeners and suspending agents, cosmetics, paper manufacturing and various mining and drilling applications.
U.S. Pat. No. 6,357,176 relates to a soil and grass seed-less sod precursor containing a non-woven bio-cellulosic fiber mat and grass sprigs. The sod precursor can be used to produce a soil-free sod which is useful for manufacturing athletic fields, golf courses and lawns. The mat may contain other materials in addition to the bio-cellulosic fiber. The mat may contain other types of fibers, such as wood fibers or synthetic organic fibers. Wood fibers may increase the water retention of the mat. Examples of organic fibers include acrylic, cellulose ester, elastomeric, olefin, polyester, polyamide and polyvinyl alcohol fibers. A synthetic organic polymer may function as a binder. The mat may also contain non-fibrous polymers, such as polysaccharides, proteins, polyacrylamide and other water retention agents. The prior art patent uses polyacrylamide to increase water retention of the mat.
U.S. Pat. No. 5,900,038 relates to a cultivation substrate and method of preparing the same. The cultivation substrate contains comminuted plants selected from among knot grass, C4 plants and plants of the cannabis and Dicksonia genuses, and is suited as a peat substitute. During the comminution process, or thereafter, additives may be added, depending on the later use of the cultivation substrate. Polyacrylamide granules, clay mineral mixtures, ground lava rock, pumice, bentonite, sand, waste paper, fly ash from brown-coal combustion, brown-coal waste and all kinds of fertilizers are suited as additives. Polyacrylamide granules improve the cultivation substrate of the invention in that it possesses a high water storing capacity for the mulch. Gelling cross-linked polyacrylamide granules, as are e.g., obtainable under the name Polywater-Aqua-Plus from Polyplant GmbH, Xanten, are especially advantageous. This prior art patent uses polyacrylamide to increase the water storing capacity of the mulch.
U.S. Pat. No. 4,337,117 relates to a synthetic sheet material resistant to decay by fungus and other microbial organisms and useful in shoe construction, mulch papers and the like. The material comprises a uniform distribution of cellulose and optionally synthetic fiber within a matrix or binder and is formed from a furnish of the fibers; a metallic quinolinolate which lends the material decay resistant; a polymer colloid such as an acrylic latex which prevents the coagulation of the subsequently added elastomeric binder by the metallic quinolinolate; and a cationic polymer which acts as a retaining agent for the metallic quinolinolate in the synthetic sheet material. The decay resistant sheet material is formed generally by a papermaking process. The cationic polymer can be polyacrylamide polymers. The polyacrylamide is used to make the sheet material decay resistant.
U.S. Pat. Nos. 5,429,741 and 5,641,458 relate to methods for treating sludge with processed cellulose material combined with another material, e.g., a surface active agent, a detergent, a surfactant, a polymer and/or an organic polymer. Cellulose flakes and a method for making them are disclosed. They can be used for animal litter or bedding, food or fertilizer. Methods for absorbing, removing, and for cleanup of a first liquid floating on or in a second liquid are disclosed, the method employing absorbent pellets. A typical surfactant useful in sludge conditioning includes emulsions such as polyacrylamide. This prior art reference used the PAM as a surfactant for the sludge treatment.
U.S. Pat. No. 5,456,733 relates to a process for producing novel mulching pellets from waste paper scrap by incorporating particulate water-insoluble, swellable, gel-forming polymer into the pellet-forming composition. The formed pellets swell and disintegrate after being spread and impregnated with water, to increase their area of ground coverage, to release any included nutrients or seeds, and to deposit polymer particles having water-absorbing properties.
The invention relates to a method for producing dry extruded mulching pellets, containing particulate waste paper and a swelling agent, capable of application by means of simple spreading devices and being highly water-absorbent and water retentive. Upon impregnation with applied water or rain, the pellets swell, expand and disintegrate to increase their area of ground coverage and provide a water-absorbing surface covering which prevents water run-off and which helps maintain moisture in the soil. The polyacrylamide increases water absorbtion of the pellets. The disintegration or coming-apart of the swollen pellets also increases the exposed surface area of the mulch and facilitates the release of seed and the release of nutrients into the soil to support germination and growth of seed and plants in the soil.
The most essential feature of the process and mulch pellets is the incorporation of a swelling agent comprising a water-insoluble, swellable, gel-forming, hydrophilic polymeric material, capable of absorbing substantial amounts of water, into pellets comprising waste paper particles. The process consists nearly entirely of particulate waste paper and contains a minor amount by weight, up to 10%, of a water soluble, film-forming, polymeric binder material, and up to 10% of a swelling agent comprising a water-insoluble, water swellable, gel-forming, hydrophobic polymeric material in particulate form, distributed throughout the pellets. The mulch pellets comprise up to about 99% by weight of particulate waste paper, which contains a small amount by weight of a water-soluble film forming binder material such as polyvinyl alcohol and/or cellulose binder material such as carboxymethyl cellulose to bind the wood fibers in the paper making process. The essential additive is the water-insoluble, gel forming, hydrophilic polymer which is uniformly mixed in a powder form. The composition is fed to a conventional pellet mill and pelletized. Examples of polymers are cross-linked polyacrylamide polymers or polyacrylate polymers. This prior art used PAM for the benefit of it's swelling ability of the pellets.
U.S. Pat. No. 6,349,499 relates to a flaked mulch product having a density similar to that of seed which is to be established, comprising an agglomerated and compacted natural raw material whose density is adjusted to within 50% of the seed. The invention provides lignocellulosic mulch product. To the raw materials may also be added various additives such as dyes and pigments, germination aids, fertilizer, and one or more surfactants and/or water absorbing substances. Surfactants may be added to encourage rapid water uptake and retention. Water absorbent materials such as polyacrylic acids, other polyacrylates, and the like may be used. In some uses, such synthetic polymers may also serve as the binder, e.g., polyacrylic acid, polyacrylamides, and various acrylate, acrylic acid, and acrylamide co- and terpolymers. This prior art reference used PAM as a binder for the mulch product.
U.S. Pat. No. 6,360,478 relates to a completely biodegradable mulch product which forms a mechanically bonded yet open fiber mulch matrix containing natural fibers and interlockable crimped natural fibers, the crimped natural fibers being crimped by a process which induces a water-resistant permanent crimp.
A polymer-based water absorbent may be dispersed throughout the fiber mulch to increase the mulch water absorption capacity. The polymer based water absorbent is preferably present at about 5% to 15% of the mulch weight. The water absorbent is preferably a powder such as a polyacrylamide-based copolymer powder that absorbs many times its own weight in water. The polymer-based water absorbent is then dispersed into the fiber mulch to increase its water absorption capacity. The water absorbent is preferably mechanically dispersed into the mixed mulch fiber-crimped synthetic fiber mulch. This prior art reference used PAM for the benefit of the mulch product.
U.S. Pat. Nos. 5,741,832, 5,779,782 and 5,942,029 relate to mechanically bonded, water absorbent fiber mulch including natural and crimped synthetic fibers that are intimately mixed to form a mechanically bonded fiber mulch. A water-absorbent polymer based material is dispersed throughout the fiber mulch to increase its water absorption capacity. The polymer based water absorbent is preferably present at about 5% to 15% of the mulch weight. The water absorbent is preferably a powder such as polyacrylamide based copolymer powder that absorbs many times its own weight in water. The polymer-based water absorbent is then dispersed into the fiber mulch to increase its water absorption capacity. The water absorption is preferably mechanically dispersed into the mixed natural fiber-synthetic fiber mulch. This prior art reference used PAM for the benefit of the mulch product.
None of the prior art references uses solid carriers as a means of applying PAM to the soil. In the prior art, PAM has been included in mulch, as a surfactant, as a water absorbent polymer, to alter the state of the mulch (cause expansion of the mulch when watered), increase mulch size to enable the mulch to better cover the seed bed, to increase the mulch's ability to absorb more water to lower the amount of excess water, and hence reduce water runoff and hence soil loss, to hold mulches together as a binder and to increase stickiness of a mulch to keep it in place.